I have probably posted this on here already, excuse me if you've read it before!!
I had a couple of attempts at night weaning and day weaning (not at the same time!) and it was horrible all round.
After a few days/nights of screaming for milk (I would cuddle him, but not feed him) he seemed to be ok. But after three weeks, both times, his behaviour took a slide in the wrong direction. He had previously been really chilled and mild mannered, and then he started tantrumming and throwing himself on the floor and the like. I went straight back to feeding on demand and it was like I pressed a button and he went back to normal.
Interestingly, I noted exactly the same pattern when I stopped carrying him in a backpack. He had just turned three and my knees were sore, so I really reluctantly put him in the buggy (I hate using the buggy, but he loves it and then won't walk). After three weeks, again, his behaviour turned for the worse. I ditched the buggy, got a pair of shoes with thicker soles and instantly he turned back into his old self. And my knees weren't sore any more!! This was 5 months ago, just around his 3rd birthday, and now he walks pretty much everywhere.
I look back at this and think WTF was I doing, why was I trying to wean him when he clearly wasn't ready, etc etc. But hindsight is great, isn't it!! I am hoping I will remember all this if I have another!!